Modular radial head prosthesis

ABSTRACT

A modular prostheses system for replacement of the radial head portion of the radius bone and methods for its use are disclosed. The system comprises a stem component comprising a anchoring portion and a mounting portion and a head component having an open channel wherein the open channel is configured to connect to the mounting portion along an assembly axis that is transverse to a longitudinal axis of the stem component.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/195,444 filed Apr. 10, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the field of injuriesto the skeleton of the elbows joint and forearm, particularly to theproximal aspect of the radius, or the radial head. Specifically, thepresent invention is drawn to a modular radial head prostheses thatenables a surgeon to assemble the prostheses during surgery without anoverhead assembly action, thus enabling a better fit with lessopportunity for mistake and less damage the surrounding bone and tissue.

BACKGROUND OF THE INVENTION

[0003] Trauma to the elbow joint frequently involves damage to theligamentous support of the elbow and fractures of the osseous structuresresponsible for the skeletal integrity of the elbow joint. The proximalaspect of the radius, or radial head, is frequently injured either inisolation or in combination with injury to other bony or ligamentousstructures of the elbow joint. The radial head may also be fractured inassociation with injuries to the forearm axis, including disruptions ofthe interosseous membrane between the radius and the ulna. Whether inisolation or in combination with other injuries, fractures of the radialhead can be difficult to treat.

[0004] Fractures of the radial head are either reconstructable orunreconstructable. Despite various technical advances in thereconstruction of radial head fractures, a certain percentage offractures are not amenable to reconstruction due to the degreecomminution or severity of the fracture. In general, unreconstructableradial head fractures result from high energy trauma and are thereforefrequently associated with significant injuries to other osseous orligamentous structures of the elbow joint or forearm. In these cases,restoration of the stabilizing function of the radial head is criticalto allow the ligaments of the elbow or forearm to heal in appropriaterelationships, thereby restoring stability to the elbow or forearm. Thisstabilizing function depends, in part, upon re-establishing theappropriate distance between the capitellum and the proximal shaft ofthe radius.

[0005] Prosthetic replacement of the radial head has evolved ratherslowly. The first widely used prosthetic radial head was introduced inthe 1970's and was composed of silicone. Silicone implants placed invarious joints throughout the body led to “silicone synovitis,” in whichthe silicone induces an inflammatory response within the joint. Further,silicone radial head prostheses were found to be incapable of resistingthe stresses to which the radial head is subjected, rendering it lessuseful in stabilizing the injured elbow or forearm.

[0006] The difficulties apparent with silicone led to experimentationwith metal radial head implants. These prostheses are fashioned from asingle piece of metal (often titanium) and include a stem and a headportion. The head portion is shaped to approximate the anatomy of theradial head. These metallic prostheses are capable of resisting thecompressive stresses to which the radial head is subjected, as has beendemonstrated in several biomechanical studies. However, significantproblems remain with these prostheses.

[0007] Anatomic and radiographic studies of the dimensions of the radialhead reveal a disparity with currently available metallic prostheses.Therefore it has been difficult to restore appropriate anatomicalignments within the elbow. Therefore restoration of the appropriaterelationship between the capitellum and proximal shaft of the radius hasbeen very difficult to achieve with these prostheses. Additionally, thefact that these prostheses are fashioned from a single piece of metalhas led to technical difficulties with insertion and removal. Surgeonshave had difficulty with matching both the size of the stem to the canalof the proximal radius and the size of the head portion to the patient'snative radial head. Removal of these non-modular components frequentlyrequires release of the lateral ligaments of the elbow and the annularligament, which binds the neck of the proximal radius to the proximalulna. Thus the elbow is frequently destabilized during removal of theseprostheses.

[0008] Designers of prosthetic joint replacements in the hip, shoulder,knee and fingers have circumvented the above mentioned difficulties byemploying the use of modular components. Modularity allows for eachaspect of a prostheses to be sized appropriately to its recipientanatomic site. The concept of modularity has only recently been appliedto commercially available radial head prostheses. Currently availablemodular radial head prostheses employ a mechanism by which the headcomponent is impacted over and onto the stem component. The surgicalexposure must therefore allow sufficient room for the head to bemaneuvered over the stem prior to being impacted. With impaction, theheight of the prostheses is decreased, resulting in a shortening of thedistance between the capitellum and the proximal shaft of the radius.Shortening this distance alters the bony anatomy such that the ligamentsof the elbow joint are not held in their appropriate lengths andtensions. Instability of the elbow or inappropriate healing of theligaments may result. Furthermore, removal of these prostheses isaccomplished in the same manner as the above mentioned metallicimplants, often requiring destabilization of the lateral aspect of theelbow joint.

[0009] In order to reap the benefits of modularity in radial headprosthetic replacement, a reliable and surgically appropriate method tosecure the stem of the prostheses to the head of the prostheses andwhich allows for accurate restoration of the appropriate spatialrelationships between the bones of the elbow is required.

SUMMARY OF THE INVENTION

[0010] It has been recognized that it would be advantageous to develop amodular prostheses system for replacement of the radial head portion ofthe radius bone that enables the surgeon to more accurately approximatethe natural radial head. Such a system can comprise a stem component anda head component. The stem component comprises an anchoring portion anda mounting portion. The head component includes an open channel orgroove, wherein the open channel can be configured to connect to themounting portion along an assembly axis that is transverse to alongitudinal axis of the stem component. In a more detailed aspect, oneembodiment, the system can further comprise a locking mechanism toprevent the open channel of the head component from indeliberatelysliding off the mounting portion once connected to the mounting portion.Additionally, a tool for inserting and removing the head component canbe present as part of the system. If present, the tool can comprise afirst arm for inserting the head component onto the mounting portion orremoving the head component from the mounting portion, by translationalforce. Additionally, a second arm is present for stabilizing the radiusbone having the anchoring portion contained within the radius bone.Thus, a translational force mechanism can be used to move the first armwhile the second arm stabilizes the radius bone.

[0011] In a further more detailed aspect, a method for fitting a damagedradius bone with a modular radial head prostheses comprises the steps ofsecuring a stem component partially within a proximal intramedullarycanal of the damaged radius bone such that a mounting portion of thestem component is exposed above the damaged radius bone; selecting ahead component that will provide a desired result; and sliding the headcomponent onto the mounting portion in a direction along an assemblyaxis that is transverse to a longitudinal axis of the stem component.

[0012] Additional features and advantages of the invention will beapparent from the detailed description which follows, taken inconjunction with the accompanying drawings, which together illustrate,by way of example, features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the accompanying drawings which illustrate embodiments of theinvention:

[0014]FIG. 1 is a front view of a stem component;

[0015]FIG. 2 is a side view of a stem component from a perspectiveperpendicular to that of FIG. 1;

[0016]FIG. 3 is a top view of a stem component:

[0017]FIG. 4 is a front view of an inner core of a head component;

[0018]FIG. 5 is a side view of an inner core of a head component from aperspective perpendicular to that of FIG. 4:

[0019]FIG. 6 is a top view of an inner core of a head component;

[0020]FIG. 7 is a front view of an outer shell of a head component;

[0021]FIG. 8 is a side view of an outer shell of a head component from aperspective perpendicular to that of FIG. 7;

[0022]FIG. 9 is an exploded perspective view of an assembly of a stemcomponent, a inner core, and an outer shell;

[0023]FIG. 10 is a perspective view of an assembled prostheses;

[0024]FIG. 11 is a front view of an assembled prostheses;

[0025]FIG. 12 is a side view of an assembled prostheses from aperspective perpendicular to that of FIG. 11.

[0026]FIG. 13 is a top view of an assembled prostheses;

[0027]FIG. 14 is a posterior oblique view of a human elbow depicting aradial head prostheses in position within a proximal radius bone andarticulating with a capitellum of a distal humerus; and

[0028]FIGS. 15 and 16 are perspective views of a tool that can be usedto insert or remove a head component from a stem component via atranslational force.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Before the present invention is disclosed and described, it is tobe understood that this invention is not limited to the particularconfigurations, process steps and materials disclosed herein as thesemay vary to some degree. It is also to be understood that theterminology used herein is used for the purpose of describing particularembodiments only, and is not intended to be limiting as the scope of thepresent invention. The invention will be limited only by the appendedclaims and equivalents thereof.

[0030] It must be noted that, as used in this specification and theappended claims, singular forms of “a,” “an,” and “the” include pluralreferents unless the content clearly dictates otherwise.

[0031] “Radial head” is defined as the essentially cylindricalprotrusion found at the proximal end of a radius bone. The term “radialhead” can also be used to modify or describe the prostheses of thepresent invention.

[0032] “Longitudinal axis” is an imaginary line that is defined by thecenter of the stem component in the direction of intramedullary canalinsertion. Thus, the “longitudinal axis” is also roughly defined asrunning parallel to a centerline running between the proximal and distalend of the radius bone.

[0033] “Transverse axis” or “assembly axis” is an axis that intersectsthe longitudinal axis. The transverse axis can be linear or non-linear.For example, if non-linear, the axis can be arcuate, provided theassembly axis intersects the longitudinal axis. Thus, angles >0_ and<180_ qualify as “transverse.” However, for practical purposes, thetransverse axis can be from 45_ to 135_ with respect to the longitudinalaxis in order to significantly benefit from the modular assemblybenefits described herein. In many instances, an essentiallyperpendicular transverse axis with respect to the longitudinal axis willbe present.

[0034] “Protuberance” can include any protuberance functional with thepresent invention, particularly with respect to certain lockingmechanisms. For example, such protuberances can be convexities.

[0035] “Concavity” is intended to describe an open space defined by amounting portion of a stem component, or an inner core. With respect toa locking mechanism, the concavity can be configured to inversely matchand accept a protuberance, though this is not required.

[0036] “Intramedullary” shall mean the within the marrow cavity of abone.

[0037] “Native” is used to describe the condition of the bone or thehead of a bone prior to damage or removal.

[0038] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the exemplaryembodiments illustrated in the drawings, and specific language will beused to describe the same. It will nevertheless be understood that nolimitation of the scope of the invention is thereby intended. Anyalterations and further modifications of the inventive featuresillustrated herein, and any additional applications of the principles ofthe invention as illustrated herein, which would occur to one skilled inthe relevant art and having possession of this disclosure, are to beconsidered within the scope of the invention.

[0039] In order to remedy the shortcomings of prosthetic radial headreplacement, a radial head prostheses is disclosed that enables theassembly without having to significantly remove or manipulate bone andtissue as part of an overhead assembly. By implementing a slidingmechanism for the assembly of the modular radial head prostheses asdescribed herein, improvement over the commercially availableprosthetics can be achieved. Specifically, a sliding mechanism inconjunction with a locking mechanism enables the secure attachment andreasonable removal of a head component from an intact stem component,without the disadvantages associated with head component insertion alongthe longitudinal axis.

[0040] With the above descriptions and definitions in mind, a stemcomponent 10 is shown in FIG. 1. Generally, the stem component 10comprises an anchoring portion 12 and a mounting portion 14. Theanchoring portion 12 is the portion that is anchored within a canal ofthe proximal radius, providing support to the radial head prosthetic asa whole. In this embodiment, the anchoring portion 12 is tapered and canbe coated or textured to allow bone ingrowth after insertion into theradius bone of a patient. The anchoring portion can be cemented, pressfit, and/or impacted into the intramedullary canal as is known by thoseskilled in the art. If a cement is used, then a cement such as, forexample, methyl methacrylate, can be used. If desired, various sizedbroaches (not shown) can be provided such that the surgeon can sound thediameter of the proximal radial shaft, thereby selecting an appropriatesized stem component. In this embodiment, the mounting portion 14 isconfigured as a dovetail shaped mount when viewed from the frontperspective shown in FIG. 1. On each side of the mounting portion 14 arestem protuberances 16 a, 16 b. Though not required, the entire stemcomponent 10 (i.e., anchoring portion 12, mounting portion 14, and stemprotuberances 16 a, 16 b) can be constructed of a rigid material such asmetal, alloy, or ceramic. If the rigid material is metal or alloy,appropriate materials can include, for example, titanium, stainlesssteel, and cobalt chrome.

[0041] Turning to FIG. 2, a side view of the stem component 10 shown. Ascan be seen, stem protrustion 16 a is configured to span a distance ofapproximately one half of the depth of the mounting portion. Stemprotuberance 16 b (not shown) is configured similarly. In FIG. 3, a topview of the stem component 10 is shown. As the mounting portion 14 isconfigured in a dovetail-type shape, the stem protuberances 16 a, 16 bare not visible from this perspective, and thus, are shown as dashedlines.

[0042] The stem component shown in FIGS. 1-3 has the dual purpose ofattaching the prostheses to the radius bone, as well as to provide amechanism to mount a head component (not shown) to the stem component.Though the head component can be a single unit, in the embodiment shownin the subsequent figures, the head component comprises an outer shelland an inner core. The practical reason for this is that it is oftendesirable to have a rigid outer shell, while having a less rigid innercore when utilizing the locking mechanism described in FIGS. 1-13.However, if the locking mechanism does not utilize compressibleprotuberances as part of the locking mechanism, the inner core can be arigid material as well. FIGS. 3-6 show an embodiment of the inner core,and FIGS. 7-8 show an embodiment of the outer shell. However, the innercore and the outer shell will generally be pre-assembled prior tosurgery.

[0043] Turning specifically to FIG. 4, an inner core 20 of a headcomponent is shown. An inner core body 22 defines the shape of the innercore 20 and can be constructed of a polymeric resin, such as, forexample, a high molecular weight polyethylene. Additionally, the outerdimension of the inner core body 22 can be cylindrical in shape.Attached to the inner core body are a pair of inner core protuberances24 a, 24 b. The inner core body 22 and the inner core protuberances 24a, 24 b define an inner core open channel or groove 26 that can beslidably connected to the mounting portion (not shown) of the stemcomponent (not shown). The inner core protuberances 24 a, 24 b can beconstructed of the same material as the body 22, though this is notrequired. Thus, the inner core body 22 and the inner core protuberances24 a, 24 b can be a single polymeric or copolymeric unit. Whatever thestructure, in this embodiment, the inner core protuberances 24 a, 24 bare constructed of a compressible material so that the inner coreprotuberances 24 a, 24 b can pass by the stem protuberances (not shown)as part of a locking mechanism.

[0044] As can be seen more clearly in FIGS. 5 and 6, the inner coreprotuberances 24 a, 24 b are configured such that they span only aportion of the depth of the open channel 26. Thus, the inner coreprotuberances 24 a, 24 b are positioned opposite the stem protuberances(not shown) such that when the head component is in place on the stemcomponent, all of the protuberances act together to form a lockingmechanism.

[0045] As shown in this embodiment, the inner core open channel 26 doesnot traverse completely through the inner core body 22. Thus, the innercore groove 26 is just long enough such that when the mounting portionof the stem component (not shown) is tracked within the inner core openchannel 26, the mounting portion and the inner core 20 will be coaxial.

[0046] In FIGS. 7 and 8, an outer shell 30 is shown. An outer shell body32 is fashioned to approximate the dimensions of a damaged or removedradial head. Thus, the outer dimension is roughly cylindrical, having aslightly concaved top portion 37 for natural articulation with thecapitellum (not shown). Because outer shell body 32 is the portion ofthe prostheses that will articulate with the capitellum upon jointmovement, this structure can be constructed of a biologically acceptablerigid material. Such a material can include, for example, metal, alloy,or ceramic. If the rigid material is metal or alloy, appropriatematerials can include, for example, titanium, stainless steel, andcobalt chrome. The outer shell body 32 also defines an inner hollow 34that accepts the inner core (not shown) when the head component is fullyconstructed. Additionally, an outer shell open channel or groove 36 ispresent that essentially matches the inner core open channel or groove(not shown) such that the mounting portion (not shown) can be insertedinto the aligned grooves. For example, the outer shell 30 and the innercore (not shown) can both be cylindrical components that define dovetailshaped grooves which substantially fits the dovetail shaped mount of thestem component. If the inner core 20 and the outer shell 30 are twodifferent materials (as in the present embodiment), then the twocomponents can be fitted together with a bonding cement, friction fit,and/or other known techniques. The outer shell open channel or groove 36can be present at only one edge of the outer shell 30 and its edges canbe tapered to avoid damage to the articular cartilage of the proximalradio-ulnar joint. As mentioned, the outer shell 30 should be composedof metal suitable for biologic implantation, and be shaped toapproximate the dimensions of the radial head. If the surgeon requiresassistance in selecting an appropriately sized head component, then anestimate of the patient's anatomy can be ascertained using plastictrials (not shown) provided for this purpose. Though not required, theedges of the outer shell groove 36 can be tapered to avoid damage to theproximal radio-ulnar joint.

[0047] Turning to FIG. 9, an exploded view of an embodiment of thepresent invention is shown. Specifically, an outer shell 30 is shownhaving an outer shell body which defines an outer shell hollow 34. Theouter shell hollow 34 fits over an outer dimension of the inner corebody 22 of the inner core 20. Once the outer shell 30 and the inner core20 are fitted together such that the outer shell open channel 36 alignswith the inner core open channel 26, the entire head component (whichcomprise these two components) can be fitted on the mounting portion 14of the stem component 10. Though not required, the locking mechanism canbe at an interface between the mounting portion 14 and the inner core20. As shown in this figure, a pair of stem protuberances 16 a, 16 b canpass over a pair of inner core protuberances 24 a, 24 b, as the innercore protuberances 24 a, 24 b are configured to compress. Once the stemprotuberances 16 a, 16 b completely pass over the inner coreprotuberances 24 a, 24 b, the stem protuberances can lock into a pair ofinner core concavities 25 a, 25 b, respectively. The concaved channels25 a, 25 b are configured in dimension to inversely match the stemprotuberances 16 a, 16 b such that a locking action occurs. Thus, anabutment of the protuberances occurs and can prevent unwanted motionbetween the head component and the stem component after the prosthesesis inserted. The protuberances also serve to prevent the head componentfrom slipping off the stem component without intentional force. e.g.,during removal by a surgeon. With this and other similar designs, thestem component can be placed in a canal of the radius bone, followed bythe fitting of the head component.

[0048]FIG. 10 shows the stem component, the inner core 20 and the outershell 30 in a completed assembly configuration. As can be seen, thecylindrical inner core 20 component fits centrally within the outershell 30. Thus, when the mounting portion 14 of stem component 10 isinserted fully within the core and shell, all three components will beconfigured coaxially. Though the outer shell 30 and the inner core 20are shown as to separate components, in practice, the outer shell 30 andthe inner core 20 can be assembled and sterilized prior to attachment tothe mounting portion 14 of the stem component 10. Thus, the surgeonwould only be required to slide the assembled head component onto thestem component 10 by lining up the open channels 26, 36 with themounting portion 14, and sliding the head component 30 into place. InFIGS. 11-13, additional views of an assembled prostheses are shown.

[0049] When assembling the head component onto the mounting portion 14,due to elastic deformation of the inner core protuberances 24 a, 24 b,all of the protuberances 16 a, 16 b, 24 a, 24 b can be slid pastopposing protuberances under sufficient translational force. In thisembodiment, the protuberances are shaped such that the force required topress the protuberances past their opposing protuberances is intentionaland reasonable, but not excessive.

[0050]FIG. 14 is a posterior oblique view of the human elbow depictingthe radial head prostheses in position within the proximal radius bone38 and articulating with the capitellum 39 of the distal humerus. As canbe seen, the anchoring portion 12 is within the medullary canal of theproximal radius 38, and the radial head 30 is articulating with thecapitellum 39 of the distal humerus.

[0051] In FIGS. 15 and 16, a tool 40 is shown that can be used with theprostheses of the present invention is shown. In FIG. 15, the tool 40 ispositioned in a first orientation with respect to proximal radius 38 forinserting the head component 30 onto the mounting portion 14. In FIG.15, the tool 40 is positioned in a second orientation with respect tothe proximal radius 38 for removing the head component 30 from themounting portion.

[0052] Specifically, with respect to FIG. 15, a first arm 42 and asecond arm 44 are shown that enable or surgeon to create translationalforce 45 to be placed on the radial head 30. The first arm 42 and thesecond arm 44 are tracked parallel to one another by a track 46 and aslider 48. The second arm 44 is connected to a handle 52 by a hinge 50.The handle 52 is designed such that by applying a squeezing force 51,translational force 45 is applied to the head component 30. Thus, inthis embodiment, the translational force mechanism is a lever. At theend of the first arm 42 is a pulling member 54 that acts to stabilizethe proximal radius 38 (or alternatively, the mounting portion 14). Atthe end of the second arm 44 is a pushing member 56 for pushing the headcomponent 30 onto the mounting portion 14.

[0053] In FIG. 16, the same tool 40 as described in FIG. 15 can be usedby flipping it upside down. Thus, the first arm 42 now acts to providethe translational force 45 and the second arm 44 stabilizes the proximalradius 38 (or alternatively, the mounting portion 14). Thus, the armsare characterized as the first arm 42 and the second arm 44 forconvenience only. It would be apparent to one skilled in the art thatthe first arm or the second arm can function as the stabilizer.Likewise, the first arm or the second arm can act to provide desiredtranslational force.

[0054] The use of such a tool is particularly helpful when a lockingmechanism such as that described in FIGS. 1-13 is in place. Locking andunlocking can be carried out as previously described. Specifically, inthe present embodiment, the tool can press the components onto oneanother while maintaining alignment of the dovetail shaped mount andgroove. In the absence of intentional and sufficient pressure totranslate the head component off of the stem component, the rigidityprovided by the polyethylene is sufficient to secure the modularcomponents to each other. Removal is accomplished by generatingsufficient translational pressure on the head component with the use ofa specially designed handle. This tool binds the far end of the headcomponent while stabilizing the proximal radius bone, and thereby thestem component. Translational force is generated which presses theprotuberances of the inner core past the protuberances of the mountingportion, thereby releasing the head component from the stem component.

[0055] A procedure that can be followed for the insertion of the modularradial head prostheses is as follows. If necessary, after resection of asubstantially unreconstructable radial head bone, a proximal edge of theradius bone can be removed by transverse sawing or some other removaltechnique. After the damaged radial head has been removed, the medullarycanal of the bone can then be broached with one or more of a series ofbroaches, the shapes of which approximate the various stem sizesavailable. Once an appropriate size stem component size has beenselected, the anchoring portion can be inserted into the proximal radiusbone such that the mounting portion protrudes from the proximal radiusbone. The head component can then selected based upon parameters such asproper ligament tensioning, circumference, and height. If desired, thisassessment can be assisted with the use of plastic trials made availablefor this purpose. After an appropriately sized head component isselected, the forearm can be rotated so that the mounting portion ispositioned to receive the head portion, i.e., an assembled outershell/inner core combination or a single piece head component. If thehead component comprises an outer shell and an inner core, the headcomponent can either be assembled at the time of manufacture or by thesurgeon. In any event, the outer shell groove and the inner core grooveshould be position such that the grooves line up for accepting themounting portion. Once the stem component is in place and the properhead component is assembled and selected, the head component is thentranslated onto the stem component fully. If a locking mechanism is usedsuch as that described in FIG. 1-13, a click will be palpable as thestem protuberances and the inner core protuberances slip fully past eachother. The prostheses will then be secure within the canal of theproximal radius bone and is positioned to articulate with the capitellumof the distal humerus.

[0056] With the above figures and surgical procedures in mind, a modularprostheses system for replacement of the radial head portion of theradius bone is disclosed comprising a stem component and a headcomponent. The stem component comprises an anchoring portion and amounting portion, and the head component can have an open channelconfigured to connect to the mounting portion along an assembly axisthat is transverse to a longitudinal axis of the stem component. Theconnection can be by a sliding motion. Though the system requires onlythat the assembly axis be transverse to the longitudinal axis of thestem component, for practical purposes, the transverse angle willgenerally be from about 45_ to 135_ with respect to the longitudinalaxis. This is due to the fact that as you approach angles closer toparallel with the longitudinal axis, the head component becomes moredifficult to put in place. In many incidences, the assembly axis willintersect the longitudinal axis at essentially a perpendicular angle.

[0057] The system can further comprise a locking mechanism to preventthe open channel of the head component from indeliberately sliding onthe mounting portion once connected to the mounting portion. This isdesirable because once the prostheses has become part of the functioningelbow joint, any slippage could require surgery for repair. Thus, theonly circumstance wherein sliding should be allowed should occur at thehand of the surgeon, with deliberate action. The locking mechanism canbe configures such as that shown in FIGS. 1-13, or by any other lockingmechanism known by those skilled in the mechanical arts. For example,after sliding the head component onto the mounting portion, the headcomponent can be locked in place with a pin or screw.

[0058] In a one embodiment, the mounting portion can be configured forallowing the head component to slide along a single axis via the openchannel. Such an embodiment is shown in he FIGS. 1-13 where thedovetail-shaped mounting portion is inversely matched with adovetailed-shaped groove. Thus, head component can be slid onto themounting portion along a single axis only.

[0059] Though not required, the head component can be inserted andremoved from the mounting portion with a specially designed tool. Thus,the system of the present invention can further comprise a tool forinserting and removing the head component while the stem component is inplace within a radial canal. Such a tool can comprise a first arm forinserting the head component onto the mounting portion or removing thehead component from the mounting portion; a second arm for stabilizingthe radius bone; and a translational force mechanism for moving thefirst arm while the second arm stabilizes the radius bone. The terms“translation” and “stabilizing” are used loosely depending on whetherthe tool is being used for insertion or removal of the head component,the arm acting to provide the translational force and the arm act toprovide stabilization can be changed. Thus, the terms are relative as tothe action, rather than to the specific structure. For example, wheninsertion of the head component is being carried out, the first armcarrying out the translational insertion does so by a pushing force, andthe second arm stabilizes the radius bone by a pulling force.Conversely, when removal of the head component is being carried out, thefirst arm removes the head component by a pulling force (i.e., the toolis flipped over, and the second arm stabilizes the radius bone by, apushing force.

[0060] As part of the system, a method for fitting a damaged radius bonewith a modular radial head prostheses is disclosed comprising the stepsof securing a stem component partially within a proximal intramedullarycanal of the damaged radius bone such that a mounting portion of stemcomponent is exposed above the damaged radius bone; selecting a headcomponent that will provide a desired result; and sliding the headcomponent onto the mounting portion in a direction along an assemblyaxis that is transverse to a longitudinal axis of the stem component.Typically, a preliminary step of removing a radial head of the damagedradius bone is carried out prior to fitting the radius bone with theprostheses of the present invention, though there can be circumstanceswhere this preliminary step is not necessary. Additionally, beforesecuring the stem component within the intramedullary canal, it may bedesirable to carry out the preliminary step of sizing the stem componentto securely fit within the proximal canal. This can be done using a setof broaches designed for this purpose. The stem component can be securedwithin the intramedullary canal by one of a number of techniquesincluding the use of cement, firm pressure into the canal, or impactingthe stem component into the canal, for example.

[0061] Once the stem component is in place, the next step of selectingan appropriate head component is carried out. Considerations can includeassessing a desired tensioning of one or more ligaments attached to theradius bone and/or assessing the height and shape of the head componentto be used. Aid in this area can be provided by the use of trialsdesigned for this purpose. Such trials can be plastic structuresconfigured to approximate the size and shape of the head component to beultimately placed on the mounting portion.

[0062] It is to be understood that the above-described arrangements areonly illustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention and the appended claims are intendedto cover such modifications and arrangements. Thus, while the presentinvention has been shown in the drawings and fully described above withparticularity and detail in connection with what is presently deemed tobe the most practical and preferred embodiment(s) of the invention, itwill be apparent to those of ordinary skill in the art that numerousmodifications, including, but not limited to, variations in size,materials, shape, form, function and manner of operation, assembly anduse may be made, without departing from the principles and concepts ofthe invention as set forth in the claims.

1. A modular prosthesis system for replacement of a portion of a bone,said modular prosthesis system comprising: a stem component having ananchoring portion and a mounting portion; and a head component defininga channel, said channel operable to be rigidly connected to saidmounting portion along an assembly axis that is transverse to alongitudinal axis of said stem component, wherein said head component issubstantially immovably fixed to said stem component.
 2. The modularprosthesis system as defined in claim 1 wherein said assembly axis issubstantially perpendicular to the longitudinal axis.
 3. The modularprosthesis system as defined in claim 1 wherein said assembly axis isbetween about 45 degrees to about 135 degrees relative to thelongitudinal axis.
 4. The modular prosthesis system as defined in claim1 wherein said assembly axis is about 0 degrees to about 180 degreesrelative to the longitudinal axis.
 5. The modular prosthesis system asdefined in claim 1 wherein said stem component is substantially formedas a single piece.
 6. The modular prosthesis system as defined in claim1 wherein said head component is formed from a first member and a secondmember.
 7. The modular prosthesis system as defined in claim 6 whereinsaid first member is an outer shell and said second member is an innercore.
 8. The modular prosthesis system as defined in claim 7 whereinsaid inner core is formed from a polymeric material and said outer shellis formed of a material selected from a group comprising ceramic,titanium, stainless steel, cobalt chrome, and a combination thereof. 9.The modular prosthesis system as defined in claim 1 wherein said headcomponent is formed from at least one of ceramic, titanium, stainlesssteel, cobalt chrome, and a combination thereof.
 10. The modularprosthesis system as defined in claim 1 wherein said channel is asubstantially elongated rectangular channel.
 11. The modular prosthesissystem as defined in claim 10 wherein said channel is a substantiallyelongated rectangular T-shaped channel.
 12. The modular prosthesissystem as defined in claim 1 further comprising a locking deviceoperable to lock said head component to said stem component.
 13. Themodular prosthesis system as defined in claim 12 wherein said lockingdevice interacts with said mounting portion and said channel.
 14. Themodular prosthesis system as defined in claim 1 wherein said mountingportion is dove tail-shaped and said channel has a corresponding matingshape.
 15. The modular prosthesis system as defined in claim 12 whereinsaid locking device is at an interface between said head component andsaid mounting portion.
 16. The modular prosthesis system as defined inclaim 15 wherein said locking device includes at least one protuberance.17. A modular prosthesis for replacement of a portion of a bonecomprising: a stem component having an anchoring portion and a mountingportion; a head component defining a channel, said channel operable tobe rigidly connected to said mounting portion along an assembly axisthat is transverse to a longitudinal axis of said stem component; and alocking device operable to rigidly lock said head component to said stemcomponent.
 18. The modular prosthesis system as defined in claim 17wherein said assembly axis is substantially perpendicular to thelongitudinal axis.
 19. The modular prosthesis system as defined in claim17 wherein said assembly axis is between about 45 degrees to about 135degrees relative to the longitudinal axis.
 20. The modular prosthesissystem as defined in claim 17 wherein said assembly axis is about 0degrees to about 180 degrees relative to the longitudinal axis.
 21. Themodular prosthesis system as defined in claim 17 wherein said stemcomponent is substantially formed as a single piece.
 22. The modularprosthesis system as defined in claim 17 wherein said head component isformed from at least one of ceramic, titanium, stainless steel, cobaltchrome, and a combination thereof.
 23. The modular prosthesis system asdefined in claim 17 wherein said mounting portion is dove tail-shapedand said channel has a corresponding mating shape.
 24. The modularprosthesis system as defined in claim 17 wherein said channel is asubstantially elongated rectangular channel.
 25. The modular prosthesissystem as defined in claim 17 wherein said locking device is formedintegral with at least one of said stem component and said headcomponent.